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Recent honey bee colony declines have brought significant attention to the need of improving honey bee health and nutrition. The importance of the microbiome of the honey bee and hive has gained significant attention in the last few years (Mattila et al. 2012 PLOS One 7(4) e35954, Anderson et al. 2011 Insectes Sociaux 58:431-444). Microorganisms associated with A. mellifera L. have been shown to inhibit the growth of A. mellifera L. pathogens (Evans and Armstrong 2006 BMC Ecol 6(4). However almost all microflora molecular work has been devoted to bacterial communities while the metagenomics of fungi has not garnered significant attention.
Some fungi have been found to be vital in the fermentation of pollen and making of the beebread. Recent research findings have shown that fungicides negatively impact the growth of symbiotic beebread microbes (Yoder et al 2002 CRC Press. p 193-214). The microbes tested were morphologically identified to the taxonomic genus level thus excluding any ascomycete anamorphs. Also, fungal microflora may differ between geographical locations, and specific strains of the same genus or species may have significantly different resistance levels. Currently, there is no regulation on fungicide treatment at full bloom when honey bees are foraging. Nectar and pollen contaminated with fungicides are carried back to the hive. Fungicide residues have been found in the wax, beebread, and pollen (Mullin et al. 2010 PLoS One 5(3): e9754). In this study we evaluated interactions between honey bee gut microbes (fungi) and their sensitivity to common fungicides found in honey bee hive matrices.
In this study we evaluated interactions between Apis mellifera L. gut microbes (fungi) and assessed their sensitivity to fungicides found in the hive matrices. Our results suggest that Chlorothalonil, Iprodione, and Boscalid inhibit growth of fungi associated with A. mellifera L. indicating the importance of further investigations into functional roles of these microbes and the effects of these fungicides in the hive. Fungicide concentrations used in this study were similar to residues found in wax and pollen. These concentrations inhibited growth of symbiotic fungi in vitro illustrating the need to know how they affect fungi in the hive and if those effects in turn would negatively impact colony health. Contrary to other studies, Chlorothalonil was detrimental to symbiotic fungal growth inhibiting nine of the ten isolates. Inconsistent trends of fungicide effects on fungal microbes, especially Mucor hiemalis, between this study and others highlights the need for further research into how exactly fungicides effect different strains of symbiotic fungi.

An antagonism test between eight of the fungal isolates against the chalk brood pathogen, Ascosphaera apis, showed that each asymptomatic fungus significantly (P<0.05) inhibited the pathogen’s growth. Measurements of the radial growth of A. apis in vitro toward and away from each microbe were compared and analyzed using a 2-Sample T-test.

Asymptomatic fungal isolates were genetically identified by sequencing of the internal transcriber spacer regions 1 and 4. Sensitivity of these isolates to important fungicides was also measured and analyzed.

This research suggests that asymptomatic honey bee microflora may play a role in the prevention of some fungal pathogens in the hive. Fungicides, while not directly affecting the honey bee, may affect the functional role of these microbes thus indirectly affecting the health or behavior of the honey bee.